Compact pressure and flow sensors for very high temperature and corrosive fluids

ABSTRACT

Heat resistant sensors equipped with any of a variety of transducers for measuring any of a variety of properties of fluids are constructed with components comprising materials that can withstand very high temperatures. Some embodiments of the sensors include a first pressure sensitive element and a second pressure sensitive element with respective first and second membranes positioned in juxtaposed relation to each other to form a capacitor. Some embodiments include a pusher that extends from the membrane toward a first electrode. Some embodiments have a housing comprising a ceramic substrate with a sensor element mounted on an inside surface of the substrate. Other embodiments have direction sensing capabilities including a heater positioned in a core material and at least three temperature sensors located at or near the peripheral surface of the core material and spaced apart angularly in relation to each other.

BACKGROUND Technical Field of the Invention

The present invention is related to sensors, and more particularly tosensors for detecting and measuring properties, such as temperature,pressure, flow rate, fluid level, and other properties in very hightemperatures and other harsh operating conditions.

State of the Prior Art

Very high temperatures, for example, as high as 1,800° C., occur in somepropulsion and power generation systems, for example, gas turbines, jetengines, coal gasifiers, concentrating solar power (CSP) heat transferfluids (HTFs), and nuclear systems. Such very high temperatures,sometimes accompanied by corrosive, oxidizing, or reducing fluids,neutron flux, or other harsh conditions, present special problems formeasuring various operating properties that are important formonitoring, control, and analyses of such propulsion and powergeneration systems, such as temperature, pressure, fluid flow, or fluidlevels. Existing sensors for measuring such properties are not able tooperate reliably for long periods of time at such very high temperaturesand harsh conditions, which are detrimental to structural andelectronics materials commonly used in such existing transducers andgauges.

The foregoing examples of the related art and limitations relatedtherewith are intended to be illustrative and not exclusive. Otherlimitations of the related art and other examples of related art willbecome apparent to those of skill in the art upon a reading of thespecification and a study of the drawings.

SUMMARY

The following embodiments and aspects thereof are described andillustrated in conjunction with systems, tools, and methods which aremeant to be examples and illustrative, not limiting in scope. In variousembodiments and implementations, one or more problems have been reducedor eliminated, while other embodiments are directed to otherimprovements and benefits.

A sensor device for detecting a property of a system, for example,temperature, pressure, fluid flow rate, or fluid level in very hightemperature fluids comprises an electrically non- conductive ceramiccore, a plurality of electrically conductive ceramic or metal electricalconductors on the core, and a transducer positioned on the core inelectrical connection with the plurality of electrically conductiveceramic or metal electrical conductors. Some embodiments of thetransducer also comprise electrically conductive ceramic elements inwhich electrical resistance varies as a function of temperature. In someembodiments of the sensor device, the ceramic electrical conductors andthe transducers can withstand temperatures as high as 1,800° C.

An embodiment of the sensor device includes a capacitive pressuresensing transducer comprising a ceramic housing and a ceramic membranethat together enclose and hermetically seal a space, wherein themembrane is positioned a spaced distance apart from a first electrodeand is resiliently deformable toward and away from the first electrodein response to pressure changes outside of the enclosed and hermeticallysealed space. A second electrode on the membrane is movable with themembrane toward and away from the first electrode in a manner that formsa variable capacitor. The first electrode is in electrical connectionwith an electrical conductor on a ceramic core, and the second electrodeis in electrical connection with another electrical conductor on thecore. In some embodiments, the ceramic core, the ceramic housing, andthe electrical conductors are made of materials that can withstandtemperatures as high as 1,800° C.

An embodiment of a sensor device for sensing pressure of a very hightemperature fluid comprises a transducer comprising a first pressuresensitive element and a second pressure sensitive element, wherein thefirst pressure sensitive element comprises a first housing that enclosesand hermetically seals a first space, one side of the first housingincluding a resiliently deformable and electrically conductive firstmembrane, and wherein the first pressure sensitive element and thesecond pressure sensitive element are positioned adjacent to each otherwith the first membrane and the second membrane positioned in juxtaposedrelation to each other a spaced distance apart from each other so as toform a capacitor. In one implementation, the first housing, includingthe first membrane, comprises an electrically conductive metal or metalalloy that can withstand very high temperatures, and the second housing,including the second membrane, comprises an electrically conductivemetal or metal alloy that can withstand very high temperatures. Inanother implementation, the first housing comprises a ceramic materialthat can withstand very high temperatures and the first membranecomprises an electrically conductive metal or metal alloy that canwithstand very high temperatures. Also, the second housing comprises aceramic material that can withstand very high temperatures, and thesecond membrane comprises an electrically conductive metal or metalalloy that can withstand very high temperatures. The first membranecomprises a ceramic material that can withstand very high temperaturesand an electrically conductive metal or metal alloy plate or coating,which can also withstand very high temperatures, formed on or attachedto an external surface of the first membrane, and wherein the secondmembrane comprises a ceramic material that can withstand hightemperatures or very high temperatures and an electrically conductivemetal or metal alloy plate or coating, which can also withstand veryhigh temperatures, formed on or attached to an external surface of thesecond membrane. A spacer can be positioned between respectiveperipheral, interfacing surfaces of the first and second housings. Thespacer can comprise any non-conductive material that can withstand thehigh temperatures or very high temperatures. Several examples of suchspacer materials may include ceramics and single crystal materials(e.g., quartz or sapphire), amorphous materials, fused crystallinematerials (e.g., fused silica, fused sapphire, etc.). A putty or pottingmaterial can also be used as the spacer.

Another capacitive pressure sensor embodiment comprises a housing thatencloses and hermetically seals a space, a side of the housingcomprising a resiliently deformable or flexible membrane that deforms orflexes in response to pressure changes outside of the housing in apressure range to be measured or monitored, wherein the housing and themembrane comprise a material that is corrosion resistant, a capacitorformed by a first electrode and a second electrode positioned inside theenclosed space and held apart from each other by one or morenon-electrically conductive stand-off supports, the first electrodebeing resiliently deformable or flexible toward or away from the secondelectrode, and a pusher in the enclosed space that extends from themembrane toward the first electrode. In one such embodiment, the pusherextends all the way from the membrane to the first electrode, and inanother such embodiment, the pusher does not extend all the way from themembrane to the first electrode.

A method of measuring pressure of a very high temperature fluidcomprises placing a transducer in the fluid, wherein the transducercomprises: (i) a first pressure sensitive element, wherein the firstpressure sensitive element comprises a first housing that encloses andhermetically seals a first space, and wherein one side of the firsthousing includes a resiliently deformable and electrically conductivefirst membrane; and (ii) a second pressure sensitive element disposedadjacent to the first pressure sensitive element, wherein the secondpressure sensitive element comprises a second housing that encloses andhermetically seals a second space, and wherein one side of the secondhousing includes a resiliently deformable and electrically conductivesecond membrane, and further, wherein the second pressure sensitiveelement is positioned and oriented such that the second membrane isjuxtaposed to the first membrane with a distance between the firstmembrane and the second membrane, applying a voltage across the firstmembrane and the second membrane, measuring capacitance between thefirst membrane and the second membrane, and determining the pressure ofthe fluid by comparing the capacitance to a predetermined correlation ofcapacitance measurements to pressures.

A flow meter embodiment for sensing flow of a high temperature fluidcomprises a transducer comprising a housing that encloses a space, saidhousing comprising a corrosion resistant material that can withstandhigh temperatures of the fluid for which flow is sensed, including oneside of the housing comprising a ceramic substrate with a surfaceoutside of the housing and another surface that is inside the housing,and a plate or cladding comprising a corrosion resistant material thatcan withstand the high temperatures of the fluid for which flow is to besensed with the flow meter sensor; and a sensor element mounted on thesurface of the ceramic substrate that is inside the housing, said sensorelement comprising an electrically resistive material, the resistivityof which varies as a function of temperature, and which can withstandthe high temperatures of the fluid for which flow is sensed. Thecorrosion resistant material can comprise a metal or metal alloy thatcan withstand the high temperatures of the fluid for which flow is to besensed with the flow meter sensor.

A flow meter sensor embodiment for detection mass flow rate and flowdirection of a fluid flow comprises an elongate tubular heater extendingcoaxially through an elongate, cylindrical core material that has alongitudinal axis and a peripheral surface; and at least three elongatetemperature sensors extending through the core material parallel to thelongitudinal axis and spaced apart angularly in relation to each otherabout the longitudinal axis and radially outward from the longitudinalaxis toward, but not all the way to, the peripheral surface of the corematerial. The core material is a modest, but overly good, heat conductormaterial, as explained in more detail below. The core material is amaterial that can withstand very high temperatures. One implementationcan include an elongate, protective sheath around the peripheral surfaceof the core material. The protective sheath can comprise a material thatcan withstand very corrosive fluids.

A method of detecting flow direction of a flowing fluid comprisespositioning an elongate core in the flowing fluid, the elongate corehaving a peripheral surface and an elongate tubular heater disposedalong a longitudinal axis of the elongate core and at least threeelongate temperature sensors disposed through the core parallel to thelongitudinal axis and spaced angularly in relation to each other aboutthe longitudinal axis and radially outward from the longitudinal axistoward the peripheral surface of the core material; measuringtemperatures at each of the temperature sensors; and determining leewarddirection as higher temperature readings and windward side as lowertemperature readings. Mass flow rate can be determined as a function ofa difference between temperature of the heat tube and the lowesttemperature reading from the temperature sensors.

In addition to the example aspects, embodiments, and implementationsdescribed above, further aspects, embodiments, and implementations willbecome apparent to persons skilled in the art after becoming familiarwith the drawings and study of the following descriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated herein and form a partof the specification, illustrate some, but not the only or exclusive,example embodiments and/or features. It is intended that the embodimentsand figures disclosed herein are to be considered illustrative ratherthan limiting. In the drawings:

FIG. 1 is an isometric view of an example heat resistant sensor devicethat is capable of withstanding very high temperatures and configuredfor mounting in any of a variety of very high temperature chambers orother harsh environments;

FIG. 2 is a top plan view of the example heat resistant sensor device inFIG. 1;

FIG. 3 is a side elevation view of the example heat resistant sensordevice in FIG. 1;

FIG. 4 is a rear elevation view of the example heat resistant sensordevice in FIG. 1;

FIG. 5 is a front elevation view of example heat resistant sensor devicein FIG. 1;

FIG. 6 is an isometric view of the example heat resistant sensor devicesimilar to FIG. 1, but with the shield removed to reveal the sensorcore, transducer, and connections;

FIG. 7 is a top plan view of the example heat resistant sensor devicesimilar to FIG. 2, but with the shield removed to reveal the sensorcore, transducer, and connections;

FIG. 8 is a front elevation view of the example heat resistant sensordevice similar to FIG. 3, but with the shield removed to reveal thesensor core, transducer, and connections;

FIG. 9 is a rear end elevation view of the example heat resistant sensordevice similar to FIG. 4, but with the shield removed;

FIG. 10 is a front end elevation view of the example heat resistantsensor device similar to FIG. 5, but with the shield removed;

FIG. 11 is an isometric view of an example core of the example heatresistant sensor device in FIG. 1;

FIG. 12 is a top plan view of the example core in FIG. 11;

FIG. 13 is a side elevation view of the example core in FIG. 11

FIG. 14 is a cross-section view of the example heat resistant sensordevice taken along section plane 14-14 in FIG. 2;

FIG. 14A is an enlarged portion 14A of FIG. 14;

FIG. 14B is an enlarged portion 14B of FIG. 14;

FIG. 15 is an enlarged perspective view of the bottom of an exampleconductive ceramic temperature transducer showing example contacts forelectrical connections to the electrical conductors of the example heatresistant sensor device in FIG. 1;

FIG. 16 is a schematic diagram of a conventional 4-wire Kelvin sensingcircuit that can be used for the transducers;

FIG. 17 is an isometric view of an alternate embodiment temperaturetransducer on the core of the example heat resistant sensor device;

FIG. 18 is an isometric view of another alternate embodiment core withduets for the electrical conductor and a wound temperature transducer;

FIG. 19 is an isometric view of another alternate embodiment core andtemperature transducer;

FIG. 20 is an isometric view of an alternate temperature sensor deviceexample with the alternate embodiment core in FIG. 19 encased in apotting material in the shield around the core;

FIG. 21 is an isometric view of another alternate core with electricconductors and transducer that can be used as a pressure transducer,flow rate transducer, or fluid level transducer;

FIG. 21A is an enlarged distal end portion of the core, electricconductors, and transducer of FIG. 21;

FIG. 22 is an isometric view of an alternative example fluid flow sensorfor measuring fluid flow rate of very high temperature fluids;

FIG. 23 is an isometric cross-section view of the example fluid flowsensor in FIG. 22;

FIG. 24 is an isometric view of the example fluid flow transducer in theexample fluid flow sensor shown in FIG. 22;

FIG. 25 is an isometric, exploded view of an example fluid flowtransducer shown in the example fluid flow sensor in FIG. 22;

FIG. 26 is an isometric cross-section view of an alternate embodimentheat resistant sensor device comprising a capacitive pressuretransducer;

FIG. 27 is an isometric view of the capacitive pressure transducer onthe core of the example heat resistant sensor device in FIG. 26;

FIG. 28 is an enlarged cross-section view of the capacitive pressuretransducer in FIGS. 26 and 27 taken along the section plane 27-27 inFIG. 27;

FIG. 29 is an enlarged cross-section view of the capacitive pressuretransducer similar to FIG. 28 but showing the membrane with one of thecapacitor electrodes flexed due to pressure on the membrane;

FIG. 30 is an isometric view of an alternative example heat-resistantcapacitive pressure sensor that is compact and resistant to hightemperature corrosive fluids;

FIG. 31 is an enlarged isometric view of the capacitive pressuretransducer of the alternate example heat-resistant capacitive pressuresensor in FIG. 30;

FIG. 32 is a further enlarged cross-section view of the alternativeexample heat- resistant capacitive pressure transducer in FIGS. 30 and31 taken along the cutting plane line 32-32 in FIG. 31;

FIG. 33 is a diagrammatic view of a metal version of the capacitivepressure transducer in FIGS. 30-33;

FIG. 34 is a diagrammatic view of the metal version of the capacitivepressure transducer of FIGS. 30-33 when exposed to an increasedpressure;

FIG. 35 is a diagrammatic view of a ceramic version of the of thecapacitive pressure transducer in FIGS. 30-33;

FIG. 36 is a diagrammatic view of the ceramic version of the capacitivepressure transducer exposed to increasing pressure;

FIG. 37 is a diagrammatic view of the ceramic version of the capacitivepressure transducer encapsulated in a potting or coating;

FIG. 38 is an isometric view of the capacitive pressure sensor in FIGS.30-33 mounted in a fitting on a probe;

FIG. 39 is an enlarged isometric view of the capacitive pressure sensorof FIGS. 30-33 mounted in the fitting on the probe;

FIG. 40 is an isometric view of the capacitive pressure sensor similarto FIGS. 38 and 39 equipped with a protective sheath;

FIGS. 41 and 42 are diagrammatic views of alternate capacitive pressuretransducers;

FIGS. 43-45 are diagrammatic views of another alternate capacitivepressure transducer with a pressure offset feature;

FIG. 46 is a graphical illustration of the offset feature of FIGS.43-45;

FIGS. 47 and 48 are diagrammatic views of an example alternatecapacitive pressure transducer that is a variation of the capacitivepressure transducer illustrated in FIGS. 41 and 42;

FIG. 49 is an isometric view of an example rotation-insensitive flowmeter sensor;

FIG. 50 is a side elevation view of the example rotation-insensitiveflow meter sensor of FIG. 49;

FIG. 51 is a front end elevation view of the examplerotation-insensitive flow meter sensor of FIG. 49;

FIG. 52 is an enlarged cross-section view of the flow transducer of theexample rotation-insensitive flow meter sensor of FIG. 49 taken alongthe cutting plane line 52-52 in FIG. 51;

FIG. 53 is an enlarged isometric view of the thermal resistive elementon the ceramic substrate of the flow meter sensor of FIG. 49;

FIG. 54 is an isometric view of an alternate examplerotation-insensitive flow meter sensor;

FIG. 55 is a side elevation view of the example rotation-insensitiveflow meter sensor of FIG. 54;

FIG. 56 is a front end elevation view of the examplerotation-insensitive flow meter sensor of FIG. 54;

FIG. 57 is an enlarged cross section view of the flow transducer of theexample rotation insensitive flow meter of FIG. 54 taken along thecutting plane line 57-57 in FIG. 56;

FIG. 58 is an isometric view of an example fluid flow sensor fordetecting mass flow rate and flow direction;

FIG. 59 is an enlarged cross section view of the example fluid flowsensor of FIG. 58; and

FIG. 60 is an enlarged distal end view of the flow transducer of theexample fluid flow sensor of FIG. 58.

DETAILED DESCRIPTIONS OF EXAMPLE EMBODIMENTS

An example heat resistant sensor device 10 illustrated in FIGS. 1-5 canbe equipped with any of a variety of transducers for measuring any of avariety of properties and is constructed of materials and in a mannerthat can withstand very high temperatures, e.g., as high as 1,800° C.,which are produced or encountered in some power systems, for example,gas turbines, jet engines, coal gasifiers, concentrating solar power(CSP) heat transfer fluids (HTFs), or nuclear systems. The heatresistant sensor device 10 can also withstand other harsh environments,including oxidizing atmospheres, reducing atmospheres, corrosiveatmospheres, and neutron irradiation,

Referring now to FIGS. 1-5 for an overview of the example heat resistantsensor device 10 and to FIGS. 6-14B for more example details, theexample heat resistant sensor device 10 comprises an elongate probe 12extending along a longitudinal axis 19 from a proximal end 13 mounted ina fitting 14 to a distal end 15. The probe 12 is configured forextending into a chamber, pipe, or other environment (not shown) where aproperty of a fluid medium (not shown), e.g., temperature, pressure,flow rate, fluid level, etc., is to be sensed for measurement or otherpurposes. For example, the fitting 14 can be configured as a pipeadapter with an externally threaded section 16 to be screwed into aninternally threaded hole or port in a chamber or pipe wall (not shown)so that the probe 12 extends into the chamber or pipe. Of course, othertypes of fittings, for example, welded, flanged, machined, or adheredfittings (not shown) instead of threaded fittings can be used. Some ofthe dimensions of components in actual implementations of the heatresistant sensor device 10 in the drawings are too thin to draw toscale, so some of the components of the example heat resistant sensordevice 10 are not shown in exact proportion in relation to othercomponents in the drawings, but persons skilled in the art canunderstand the basic concepts shown and described.

The probe 12 of the example heat resistant sensor device 10 comprises anon-electrically conductive ceramic core 20, which is best seen in FIGS.6-8 and 11-14, along with a transducer 22, electrical conductors 24, 25,26, 27, and electrical connections, which will be described in moredetail below. In this example heat resistant sensor device 10, thetransducer 22 is mounted on the core 20, and the electrical conductors24, 25, 26, 27 are positioned on and extend longitudinally along thecore 20 into electrical connection with the transducer 22, but otherconfigurations can be used. Several examples of other configurations aredescribed below. An optional shield 18, which is best seen in FIGS. 1-3,surrounds and protects the core 20, transducer 22, and electricalconductors 24, 25, 26, 27.

The shield 18 can be pressure sealed to the fitting 14 to isolate theinterior of the shield 18 from the pressure outside the shield 18 ifdesired, or the interior of the shield 18 can be connected in fluid flowcommunication with the environment outside the shield 18, for example,by providing a hole 17 through the distal end of the shield 18 (seeFIGS. 1, 5, and 14). Four electrical conductors 24, 25, 26, 27 areillustrated on the core 20 in FIGS. 6-8 and 14, but any number ofelectrical conductors can be provided to accommodate whatever kind oftransducer 22 that may be used for a particular purpose. The ceramiccore 20 is electrically non-conductive and provides a substratestructure for supporting the electrical conductors 24, 25, 26, 27 andthe transducer 22. The electrical conductors 24, 25, 26, 27 can bedeposited on the core 20 in thicknesses in a range of 1,000 microns tofive angstroms. Any appropriate thin film process (for example, chemicalvapor deposition, physical vapor deposition, sputtering, atomic layerdeposition, molecular beam epitaxy, evaporation, ion implantation,chemical films synthesis, chemical solution deposition, spin coating,dip coating, cathodic arc deposition, and other known thin filmdeposition process) or appropriate thick film process (for example,screen printing of conductive ink, stenciling, electroplating, and thelike), which are well-known to persons skilled in the art, can be usedto deposit the electrical conductors 24, 25, 26, 27. Distinct wires (notshown) could also be used in some implementations.

Because of the very high temperature environments and applications forwhich the example heat resistant sensor device 10 is intended, the core20 and electrical conductors 24, 25, 26, 27 are made of materials thatcan withstand such high temperatures, e.g., 1,000° C., 1,400° C., oreven 1,800° C. Accordingly, the ceramic core 20 can be fabricated usingtraditional High Temperature Cofired Ceramic technology (HTCC) or LowTemperature Coined Ceramic (LTCC) technology comprising, for example,but not for limitation, alumina (high and low purity), zirconia (yttriadoped and non-doped), beryllium oxide (beryllia, BeO), hafnium oxide(haft is magnesium oxide, silicon carbide, silicon nitride, sapphire,amorphous silica, or quartz. For example, silicon nitride or LTCC glassceramics, glass ceramic composite, or glass bonded ceramics can be usedfor a core 20 that must withstand temperatures up to 1,000° C.; alumina,aluminum nitride, silicon carbide or magnesium oxide can be used for acore that must withstand temperatures up to 1,400°C.; and sapphire,hafnium, or beryllium oxide can be used for a core 20 that mustwithstand temperatures up to 1,800° C. While not shown, the ceramic core20 could include a laminated or other composite structure comprising ahigh temperature refractory or Noble metal along with the ceramic aslong as electrical insulation for the electrical conductors 24, 25, 26,27 is maintained.

The electrical conductors 24, 25, 26, 27 can be metallic conductors orconductive ceramic conductors. Appropriate materials for electricalconductors 24, 25, 26, 27 in probes 12 that can withstand temperaturesas high a 1,800° C. may include, for example, all platinum group metals,alloys comprising platinum (Pt) or rhodium (Rh), all refractory metals,e.g., niobium (Nb) or tungsten (W), alloys comprising refractory metals,e.g., molybdenum silicide (MoSi₂), and very high temperature (VHT)polymer derived ceramics, e.g., SiBCN or SiAlCN. Other electricallyconductive ceramics for the electrical conductors 24, 25, 26, 27 inprobes 12 that can withstand temperatures as high as 1,800° C. mayinclude lanthanum-based ceramics, titanium diboride (TiB₂), titaniumdisilicide (TiSi₂), refractory carbides or borides, indium tin oxide(ITO), conductive zirconia, or doped or undoped silicon carbonitride(SiCN). Gold (Au), silver (Ag), or palladium (Pd) can be used for lowertemperature applications, e.g., up to 1,000° C. The electricalconductors 24, 25, 26, 27 can be applied on the ceramic core 20 in thickfilms or thin films with any known suitable technique, for example,screen printing, stenciling and sintering thick film inks, chemicalvapor deposition, physical vapor deposition, sputtering, organometallicdeposition, or thermal decomposition of polymers. The fittings 14 andshield 18 are also made of high temperature metals or alloys, including,for example, stainless steel or nickel alloys such as Hastalloy orInconel, although the shield 18 may also be ceramic or sapphire in someembodiments.

As best seen in FIGS. 14, 14A, and 14B, the probe 12 is mounted in thefitting 14. The proximal end 28 of the core 20 is connected mechanicallyto the fitting 14. The electrical conductors 24, 25, 26, 27 on the core12 are connected electrically to a cable 30, which extends into anopposite end of the fitting 14 from the probe 12 to carry electricalsignals from the transducer 22 to signal processing circuitry (notshown), which can be located remote from the probe 12. Inside thefitting 14, an end 32 of the cable 30 extends into a proximal end 34 ofa thin cylindrical sheath 36, and the proximal end 28 of the core 20extends into the distal end 38 of the thin cylindrical sheath 36. Thecable 30 can be a mineral-insulated cable that can withstand very hightemperatures, A plurality of electrically conductive wires, for example,four wires 40, 42, 44, 46, of the cable 30 (two of which are visible inFIGS. 14 and 14A) extend through the thin cylindrical sheath 36 forconnection to electrical conductors 24, 25, 26, 27 on the core 20 of theprobe 12. Some electrical conductor materials, for example, thick filminks used in High Temperature Cofired Ceramic (HTCC) processing, do nothave a strong adherence to the core 20, so direct connection of thecable wires 40, 42, 44, 46 to the respective electrical conductors 24,25, 26, 27 on the core 20 may not be sufficiently secure. The exampleelectrical connection of the cable wire 40 to the electrical conductor25 on the core 20 shown in FIG. 14A comprises a braze or weldinterconnect 48 of a metal tab 49, wherein the braze interconnectcontacts and adheres to both the electrical conductor 25 and core 20,which makes a strong mechanical bond of the metal tab 49 to both thecore 20 and the electrical conductor 25. The cable wire 40 is brazed 48to the metal tab 49 for a strong mechanical and electrical connection ofthe cable wire 40 to the electrical conductor 25. All of the materialsused in the connection components are compatible with the very hightemperature range described above. The remaining cable wires 42, 44, 46can be connected to the respective remaining electrical conductors 24,26, 27 in the same manner as this connection of cable wire 40 to theelectrical conductor 25.

With all of the cable wires 40, 42, 44, 46 connected to respectiveelectrical conductors 24, 25, 26, 27, the sheath 36 can, but does nothave to, be filled with an electrically non- conductive ceramic cementor potting compound 39 and allowed to solidify around the proximal end28 of the ceramic core 20 and around the cable wires 40, 42, 44, 46 toinsulate the cable wires 40, 42, 44, 46 electrically and to form astrong mechanical connection between the cable 30 and the proximal end28 of the core 20. Ceramic cements and potting compounds comprisingalumina, zirconia, silica, hafnia, magnesia, beryllia, and others areavailable commercially. The potting material 39 also pressure seals theconnection of the core 20 and electrical conductors 24, 25, 26, 27 tothe cable 30 to provide a pressure sealed feed-through of the cablewires 40, 42, 44, 46 in the fitting 14 to enable the heat resistantsensor device 10 to be used with the probe 12 in chambers, pipes, orother spaces in which the pressure is different than the ambientpressure outside such chambers, pipes, or other spaces. A machined orextruded solid ceramic plug comprising any of those ceramic materialscould be used instead of the ceramic cement or potting material. All ofthe materials used in the connection are high temperature compatible.

As explained above, the transducer 22 in the example heat resistantsensor device 10 is shown in FIGS. 6-8, 14, and 14B mounted on thedistal end 29 of the core 30 and can be any of a variety of transducersthat can sense any of a variety of conditions, for example, temperature,pressure, or other conditions. To measure temperatures in the very hightemperature range of, for example, 800° C. to 1,800° C., the transducer22 can be, for example, a temperature transducer 50 as shown in FIGS.14B and 15 based on the temperature dependent electrical resistance ofan electrically conductive ceramic, such as SiBCN, SiAlCN, or MoSi₂.Other ceramic materials with temperature dependent resistivities canalso be used for the temperature sensing element 50, for example,silicon carbide, boron carbide, hafnium carbide, zirconia,lanthanum-based ceramics, and others. Graphite and indium tin oxide(ITO) also have resistances that vary as a function of temperature andmay be used as the temperature transducer 22 for some applications, forexample, directly measuring temperature or as part of thermal basedpressure, vacuum, or flow sensing strategies where the temperature ofthe sensing element varies in response to the target measurand.Accordingly, as shown in FIG. 15, an example temperature transducer 50made of such a ceramic in which the electrical resistance varies as afunction of temperature is provided with a plurality of electricallyconductive contacts, e.g., two contacts 51, 52, placed at respectivepositions apart from each other on the bottom surface 53 of thetemperature transducer 50 that will align with and contact appropriateelectrical conductors 24, 25, 26, 27 on the core 20 when the temperaturetransducer 50 is placed on core 20 as shown in FIG. 14B and as explainedin more detail below. The electrical resistance of the ceramic materialof the temperature transducer 50 between the respective contacts 51, 52varies as a function of temperature, so a voltage applied across the twocontacts 51, 52 will result in temperature dependent variation incurrent according to Ohm's law, which can be detected by electroniccircuitry remote from the heat resistant sensor device 10. Conversely, aconstant current applied between the two contacts 51, 52 will result intemperature dependent variation in voltage according to Ohm's law, whichcan be detected by electronic circuitry remote from the heat resistantsensor device 10.

A conventional 4-wire Kelvin sensing circuit as illustrated in FIG. 16can be used for driving and obtaining signals from the temperaturetransducer 50 for determining resistance of the ceramic material of thetemperature transducer 50, which is indicative of temperature. Two leadsare used to drive a known current across the subject resistorR_(subject) (e.g., the temperature transducer 50 in FIGS. 14A and 14B),which results in a voltage potential across the subject resistorR_(subject). A second pair of leads is used to measure that generatedvoltage potential across the subject resistor R_(subject). Using Ohm'slaw, i.e., resistance equals voltage divided by current (R=V/I),resistance of the subject resistor R_(subject) (e.g., temperaturetransducer 50) can be determined by dividing the voltage measurementfrom the voltmeter by the amperage (current).

An example implementation of such a 4-wire Kelvin sensing circuit to thetemperature transducer 50 and probe 12 of the example heat resistantsensor device 10 can be seen with reference to FIGS. 11, 12, 1413, 15,and 16. The example temperature transducer 50 shown in FIG. 15 has twoelectrically conductive contacts 51, 52 on its bottom surface 53positioned so that, when the temperature transducer 50 is positioned onthe core 20, the contact 51 on the bottom surface 53 of the temperaturetransducer 50 is connected electrically to both the electric conductor24 and the electric conductor 25. Similarly, the contact 52 on thebottom surface 53 of the temperature transducer 50 is connectedelectrically to both the electric conductor 26 and the electricconductor 27. Accordingly, the two outside electrical conductors 24, 27are used to drive a known current across the temperature transducer 50between the contacts 51, 52, which results in a voltage potential acrossthat ceramic material, In one embodiment, the temperature transducer 50may be an electrically conductive ceramic material, but other materialswith temperature dependent resistivities that are capable ofwithstanding the very temperatures described above could also be used.The two inner electrical conductors 25, 26 are used to measure thatgenerated voltage potential across the material of the temperaturetransducer 50 between the contacts 51, 52. Alternatively, the innerconductors 25, 26 could be used to drive the known current across thetransducer 50 and the outer conductors 24, 27 could be used fordetecting the voltage. The volt meter, ammeter, and other circuitcomponents can be positioned remote from the example heat resistantsensor device 10, connected to the temperature transducer 50 by thecable 30 (described above). Using Ohm's law, i.e., resistance equalsvoltage divided by current (R=V/I), the resistance of the temperaturetransducer 50 can be determined, and the resistance can then becorrelated empirically to temperature.

The temperature transducer 50 can be fastened to the distal end 29 ofthe core 20 with an epoxy adhesive or any other convenientinstrumentality that can withstand the very high temperature range,e.g., 650° C. to 1,800° C. Of course, other electrical connections canbe used to connect the temperature transducer 50 to the electricalconductors 24, 25, 26, 27 on the ceramic core 20.

In an alternate embodiment shown in FIG. 17, a temperature transducer 60(outlined by phantom line circle) is formed on the core 20 along with,and as an extension of the electrical conductors 24, 25, 26, 27 on theceramic core 20, Like the ceramic temperature transducer 50 describedabove, this example temperature transducer 60 is configured as a 4-wireKelvin sensing circuit with the two outside electrical conductors 24, 27connected to leads 61, 62 of the resistive element 63 to drive a knownelectric current through the resistive element 63. The two insideelectrical conductors 25, 26 are also connected electrically to theleads 61, 62 for detecting the voltage potential across the resistiveelement 63 that results from the current flow in the resistive element63 according to Ohm's law as explained above. The resistive element 63can, but does not have to, be made of the same conductive material asthe electrical conductors 24, 25, 26, 27 and fabricated on the core 20in the same way. Of course, the wiring arrangements could be varied,such as connecting the inside conductors 25, 26 to the leads 61, 62 andusing the outside conductors 24, 27 for voltage detection.

Another example embodiment temperature sensor 80 shown in FIG. 18illustrates a resistive wire temperature sensing element 82 wound arounda distal end piece 84 of a ceramic core 86, which can be made with thesame materials as the core 20 examples described in other exampleembodiments above. In this example embodiment temperature sensor 80, thedistal end piece 84 extends from a cylindrical section 88 of the ceramiccore 86, and the electric conductors 94, 95, 96, 97 extend throughrespective ducts 104, 105, 106, 107 in the cylindrical section 88. For a4-wire Kelvin sensing circuit, the electrical conductors 94, 97 in theFIG. 18 embodiment 80 extend into, or may be connected electrically to,the opposite first and second ends 91, 92 of the resistive wiretemperature sensing element 82 to drive a known electric current throughthe resistive wire temperature sensing element 82, and the electricalconductors 95, 97 are also connected by jumpers 98, 99 to the respectiveopposite first and second ends 91, 92 of the resistive wire sensingelement 82 for detecting the voltage potential across the resistive wiresensing element 82 that results from the current flow in the resistivewire sensing element 82 according to Ohm's law as explained above.

Depending on the application, the electrical conductors 94, 95, 96, 97and the resistive wire sensing element 82 can be made with any of thematerials described above for the electric conductors 24, 25, 26, 27 inthe FIGS. 1-17 examples or the electric conductors 24′, 25′, 26′, 27′for the FIG. 19 embodiment described below. Also, the cylindrical coresection 88 with the duets 104, 105, 106, 107 can be used in any of theother example sensor device embodiments described above or below.Likewise, any of the other core embodiments, for example core 20, can beused instead of the ceramic core 86 in the FIG. 18 embodiment.

Another alternate embodiment temperature transducer 68 shown in FIG. 19comprises an electrically conductive ceramic bar 70, a first end 71 ofwhich is sandwiched between two electrical conductors 24′, 25° thatprotrude from the distal end 29 of the core 20 and a second end 72 ofwhich is sandwiched between the other two electrical conductors 26′,27′. In this alternate FIG. 19 embodiment, the electrical conductors24′, 25′, 26′ 27° have somewhat different structures and are notpositioned on the core 20 the same as the electrical conductors 24, 25,26, 27 in the embodiments shown in FIGS. 1-16, but, except for the prime(′) designation, the numbering in this description is the same becausethe function is the same. For instance, for a 4-wire Kelvin sensingcircuit, the electrical conductors 24′, 27′ in the FIG. 19 embodimentare connected respectively to the first end 71 and the second end 72 ofthe electrically conductive ceramic bar 70 to drive a known electriccurrent through the bar 70, and the electrical conductors 25′, 26′ arealso connected to the respective opposite first and second ends 71, 72of the bar 70 for detecting the voltage potential across the bar 70 thatresults from the current flow in the bar 70 according to Ohm's law asexplained above.

In the embodiment shown in FIG. 19, electrical conductors 24′, 27′ arepositioned on the top side of the core 20, and the electrical conductors25′, 26′ are shown positioned on the bottom side of the core 20,although other arrangements may be used. Electrical connections of theelectrical conductors 24′, 25′, 26′, 27′ (or mid-portion transitionelectrodes 24″, 25″, 26″, 27″) to the cable 30 (not shown) can beaccomplished in the same manner as shown in FIGS. 14 and 14A anddescribed above. Depending on the application, the electrical conductors24′, 25′, 26′, 27′ in the FIG. 19 embodiment can be made with any of thematerials as described above for the conductors 24, 25, 26, 27 in FIGS.6-14B.

An example alternate embodiment temperature sensor 110 is shown in FIG.20 equipped with the example temperature transducer 68 of FIG. 19. Inthis example temperature sensor 110, the space in the shield 18 isfilled with a potting material 112 for the purpose of making the probe12 more rigid and more rugged. For example, the potting material 112adds effective thickness and mass, thus strength, to the core 29, whichreduces effects of vibrations and inertial shock. The potting material112 can also be an electrical insulator to help prevent electricalcomponents from touching and shorting to other electrically conductivecomponents, In this example temperature sensor 110, the electricconductors 24′, 25′, 26′, 27′ are the same as described above, but, toenable the distal portion 114 of the probe 12 to withstand and functionin the 1,400° C. to 1,800° C. temperature range as indicated in FIG. 20,the electric conductors 24′, 25′, 26′, 27′ can be made with any of thenoble metals, refractory metals, or conductive ceramic materialsdescribed above that can withstand temperatures at least as high as1,800° C. Optional transition conductors 24″, 25″, 26″, 27″ (shown inFIG. 19, but only two of which are visible in FIG. 20) can be providedin the mid-portion 116 of the probe 12 for several reasons. For example,if the mid-portion 116 of the probe 12 is only exposed to moderatelylower temperatures than the distal portion 114, e.g., only in a range of800° C. to 1,400° C. in the mid- portion 116 while the distal portion114 is exposed to temperatures in a higher range of 1,400° C. to 1,800°C. as indicated in FIG. 20, it may be desirable or more practical to usetransition conductors 24″, 25″, 26″, 27″ made of less expensive,transition electrical conductors 24″, 25″, 26″, 27″ in the mid-portion116 of the probe 12, especially when conductors 24′, 25′, 26′, 27′ inthe distal portion 114 of the probe 12 are made from precious materialslike platinum. It may also be an attractive option to use transitionelectrical conductors 24″, 25″, 26″, 27″ made of a more rugged materialin the mid-portion 116, when conductors 24′, 25′, 26′, 2′ in the distalportion 114 of the probe 12 are made from brittle ceramic materials. Itmay also be an attractive option to use transition electrical conductors24″, 25″, 26″, 27″ made of a material that is easier to fabricate, whenconductors 24′, 25′, 26′, 27′ in the distal portion 114 of the probe 12are made from process-intensive materials like SICN (doped or undoped).Such precious, brittle, or difficult to produce or use materials may beneeded for conductors 24′, 25′, 26′, 27′ at the distal end of the probe12, where operating temperatures may reach 1,400° C. to 1,800° C., butother materials as explained above can be used for the transitionelectrical conductors 24″, 25″, 26″, 27″ in the mid-portion 116 wheretemperatures are still high, but not quite so high as at the distal end114, for example, less than 1,400° C. The optional transition conductors24″, 25″, 26″, 27″ connect the respective electric conductors 24′, 25′,26′, 27′ electrically to the respective electrical conductors in thecable 30. While the two transition conductors 26″, 27″ are not visiblein FIG. 20, portions of them are illustrated in FIG. 19, and personsskilled in the art will understand that such two transition conductors26″, 27″ can be connected electrically to the electric conductors 26′,27′ in the same manner as the two transition conductors 24″, 25″ connectelectrically to the electric conductors 24′, 25′.

An alternative example ceramic core 120 shown in FIGS. 21 and 21A withelectrical conductors 124, 125, 126, 127, and transducer 122 is usablein a probe 12 as a temperature sensor with or without the optional hole17 in the optional shield 18 (FIGS. 1-5) similar to the transducer 60 inthe FIG. 17 embodiment. Alternatively, this alternative example ceramiccore 120 and transducer 122 in FIGS. 21 and 21A can be used as apressure, fluid flow, or fluid level sensor. Like the exampletemperature transducer 60 in FIG. 17, the transducer 122 in FIGS. 21 and21A comprises a thermal resistive element 123 in which electricalresistance varies as a function of temperature. Also, like thetemperature transducer 60 and electrical conductors 24, 25, 26, 27 inthe FIG. 17 embodiment, the electrical conductors 124, 125, 126, 127 andtransducer 122 in this FIG. 21 example embodiment are configured as a4-wire Kelvin sensing circuit with the two outside electrical conductors124, 127 connected to leads 128, 129 of the thermal resistive element123 of the transducer 122 to drive an electric current through thethermal resistive element 123. The two inside electrical conductors 125,126 are also connected electrically to the leads 128, 129 of a thermalresistive element 123 for detecting the voltage potential across thethermal resistive element 123 that results from the current flow in thethermal resistive element 123 according to Ohm's law as explained above.Alternatively, the inside conductors 125, 126 can be used to drive theelectric current, and the voltage can be detected on the outsideconductors 124, 127. The thermal resistive element 123 can be made ofthe same conductive material as the electrical conductors 24, 25, 26, 27described above for the sensor device 10 in FIGS. 1-15 and can befabricated on the non-conductive ceramic core 120 in the same way as theelectrical conductors 25, 25, 26, 27 are fabricated on the core 20. Inthat 4-wire Kelvin circuit configuration, the transducer 122 can be usedas a temperature sensor transducer in the same manner as the transducer60 described above for the FIG. 17 embodiment.

For use of the example ceramic core 120, electrical conductors 124, 125,126, 127, and transducer 122 in FIGS. 21 and 21A as a fluid pressuresensor, the thermal resistive element 123 of the transducer 122 ispositioned on the ceramic core 120 in a place and manner that exposesthe thermal resistive element 123 of the transducer 122 to a fluid (notshown in FIGS. 21 and 21A) for which the pressure is to be measured, andthe transducer 122 functions as a wire anemometer for sensing ormeasuring pressure of the fluid. In FIGS. 21 and 21A, the thermalresistive element 123 of the transducer 122 is positioned adjacent tothe distal end 131 of the ceramic core 120, and, if an optional shield18 is provided (see FIGS. 1-5), the shield 18 can be provided with thehole 17 (see FIGS. 1 and 5) to allow fluid pressure inside the shield 18around the thermal resistive element 123 (FIGS. 21 and 21A) to equalizewith the fluid pressure outside the shield 18 that is to be sensed ormeasured. The ceramic core 120 can be made from any of the materialsdescribed above for the core 20 in FIGS. 1-44. The electric conductors124, 125, 126, 127 and the thermal resistive element 123 can be made ofthe same conductive material as the electrical conductors 24, 25, 26, 27in FIGS. 1-14 and can be fabricated on the core 120 in the same way asthe electrical conductors 24, 25, 26, 27 are fabricated on the core 20in FIGS. 1-14.

The electric current driven through the thermal resistive element 123 ofthe transducer 122, for example, by the 4-wire Kelvin sensing circuitdescribed above, creates heat in the thermal resistive element 123,which dissipates by conduction into the molecules of the surroundingfluid. The electrical resistance of the thermal resistive element 123rises as the temperature of the thermal resistive element 123 increases,and the electrical resistance of the thermal resistive element 123decreases as the temperature of the thermal resistive element 123decreases. Therefore, as the heat generated by the electric current inthe thermal resistive element 123 is dissipated away from the thermalresistive element 123 by conduction into the fluid molecules surroundingthe thermal resistive element 123, the thermal resistive element 123cools and electrical resistance in the thermal resistive element 123decreases. The higher the pressure of the fluid surrounding the thermalresistive element 123, the more fluid molecules there are to conductheat away from the thermal resistive element 123. Conversely, the lowerthe pressure of the fluid surrounding the thermal resistive element 123,the fewer molecules there are to conduct heat away from the thermalresistive element 123. Consequently, higher pressure fluid provides moreconduction of heat away from, thus more cooling of, the thermalresistive element 123, and lower pressure fluid provides less conductionof heat away from, thus less cooling of, the thermal resistive element123. Therefore, electrical resistance of the thermal resistive element123 varies as a function of the pressure of the gas (e.g., inverserelationship), and the resulting higher or lower electrical resistancein the thermal resistive element 123 can be detected and measured in anumber of ways that are well-known to persons skilled in the art. Forexample, but not for limitation, if a constant current is driven throughthe thermal resistive element 123, lower resistance resulting from ahigher gas pressure is manifested in a lower voltage across the thermalresistive element 123, and higher resistance resulting from a lower gaspressure is manifested in a higher voltage across the thermal resistiveelement 123. Such voltage changes are detectable and measureable.Conversely, if a current is driven through the thermal resistive element123 at a constant voltage, lower resistance resulting from a higher gaspressure is manifested in a higher current flow through the thermalresistive element 123, and higher resistance resulting from a lower gaspressure is manifested in a lower current flow through the thermalresistive element 123. The voltage or current measurements can beassociated empirically to specific pressure values.

The ceramic core 120 has an aperture 130 to at least partially isolatethe thermal resistive element 123 adjacent to the distal end 139 of thecore 20 from the rest of the core 20, which minimizes conduction of heatgenerated in the thermal resistive element 123 into the rest of the core20. Any heat lost to the core 20, instead of being dissipated into thesurrounding fluid medium, is heat loss that is not affected by, thus isinsensitive to, a pressure change in the fluid medium. Therefore, theaperture 130, which minimizes heat loss to the core 20, enhancessensitivity of the transducer 122 to pressure changes in the surroundingfluid medium.

While not visible in the isometric views of FIGS. 21 and 21A, a separatetemperature sensor circuit, for example, but not for limitation, thetemperature transducer 60, electrical conductors 24, 25, 26, 27, andother components shown in FIG. 17, can be placed on the bottom of thecore 120 in FIG. 21 to provide temperature compensation for the pressuremeasurements made with the transducer 122. Temperature compensation isprovided by measurement of the temperature of the temperature transduceron the core 120 independent of the gas pressure, e.g., independent ofany change in electric signals due to heat dissipation from thetransducer 122 into the gas, and then using that measurement to correctsignals from the pressure transducer 122 due to temperature as opposedto pressure. Analog circuits and digital signal processing forimplementation of temperature compensation for signals from anemometerpressure sensors are well-known to persons skilled in the art and can beused for implementation of temperature compensation for pressuremeasurements with the transducer 122.

Any of the example transducers 50, 60, 68, 80, 122 described above canalso be used as flow rate sensors. Referring to the transducer 122 inFIGS. 20 and 21A as an example, the thermal resistive element 123 of thetransducer 122 can be exposed to a flowing fluid for which flow rate isto be measured. Alternatively, the thermal resistive element 123 can beplaced in contact with an effective heat transfer material (not shown inFIGS. 21 and 21A) that is exposed to the flowing fluid and that conductsheat from the thermal resistive element 123 to the flowing fluid. Thefaster the fluid flows over or in contact with the thermal resistiveelement 123 or the heat transfer material (not shown), the faster heatgenerated in the thermal resistive element 123 from current flow in thethermal resistive material 123 is conducted away from the thermalresistive element 123. Conversely, the slower the fluid flows over or incontact with the thermal resistive element 123 or the heat transfermaterial (not shown), the slower heat generated in the thermal resistivematerial 123 from current flow in the thermal resistive material 123 isconducted away from the thermal resistive element 123. Therefore,according to the same principle described above for the pressuremeasuring application of the transducer 122, the faster the fluid flows,the more the heat that is generated in the thermal resistive material123 dissipates and the thermal resistive material cools, which resultsin lower electrical resistance in the thermal resistive material 123.Conversely, the slower the fluid flows, the slower the heat from thethermal resistive material 123 dissipates, which results in higherelectrical resistance in the thermal resistive material 123. Suchchanges and variations are detectable and measureable electrically, forexample, in voltage or current measurements, as explained above, and areusable for flow rate measurements. Temperature changes in the flowingfluid affect the voltage or current measurements. Therefore atemperature sensor (not shown) for temperature compensation as describedabove can be used to correct the voltage or current measurements foreffects of temperature on the fluid flow measurements. The voltage orcurrent measurements can be associated empirically to specific flow ratevalues for particular fluids.

The optional shield 18 (FIGS. 1-5) would interfere with flow of thefluid over the transducer 122, so it may not be suitable for flow ratesensor applications of the probe 12, at least not without modificationsor variations. Accordingly, an example flow meter sensor 140 with amodified probe 142 that accommodates those requirements is shown inFIGS. 22-24. In this example flow meter sensor 140, an elongate barrel144 has a proximal end 146 mounted on the fitting 14 for extending intoa chamber or pipe (not shown) in which a fluid flows, and a shield 145is mounted on the distal end 148 of the barrel 144. The barrel 144houses and supports a transducer 150 that extends outwardly from thedistal end 148 of the barrel 144 into the shield 145. The shield 145 hasan aperture 147 extending transversely through the shield 145 to allow afluid to flow over the transducer 150, as indicated by the flow arrow149 in FIG. 22, while the shield 145 provides some protection for thetransducer 150.

The transducer 150 in the example flow meter sensor 140 is sandwichedbetween a base core section 152 and a cover core section 154 laminatedtogether to form a core 156 that supports and protects the transducer150 and associated electrical conductors 158, 160 and contact terminals164, 165, 166, 167. While any of the example cores 20, 86, 120 andtransducers 22, 50, 60, 68, 122 described above could be used, thetransducer 150, with the thermal resistive element 168 sandwichedbetween the base core section 152 and the cover core section 154,provides some additional protection for the thermal resistive element168, thus durability and ruggedness. In this example, the base coresection 152 and cover core section 154 provide a heat transfer function,i.e., heat transfer materials, to transfer heat from the thermalresistive element 168 to the fluid flowing over the transducer 150,since the cover core section 154 and the base core section 152 preventdirect contact of the fluid flow 149 with the thermal resistive element168. In this example, two of the contact terminals 164, 165 areconnected to one of the electrical conductors 158 and the other twocontact terminals 166, 167 are connected to the other electricalconductor 160, and the conductors 158, 160 are connected to oppositeends of the thermal resistive element 168 of the transducer 150 toprovide a 4-wire Kelvin sensing circuit as explained above. The fasterthe fluid flows over the transducer 150, the more heat is dissipatedfrom the thermal resistive element 168, which changes the resistance ofthe thermal resistive element 168, as explained above. As also explainedabove, such changes in resistance can be detected and measured bychanges in voltage or current flow, which is indicative of the fluidflow rate of the fluid flow 149 over the transducer 150.

A potting compound 170, e.g., ceramic cement, similar to the ceramiccement or potting compound 39 in FIG. 14A described above, is providedto anchor the proximal portion 172 of the core 156 in the barrel 144 andto provide a seal between the outside of the barrel 144 and the insideof the barrel 144, where the cable 30 is positioned. The cable 30extends from the rear end of the fitting 14, which would be outside of achamber or pipe (not shown) in which the flow meter sensor 140 would bemounted for use, through the fitting 14 and through a bore 174 in thebarrel 144, to or almost to the proximal end of the core 156, where thewires in the cable 30 are connected to the contact terminals 164, 165,166, 167 on the core 156. Therefore, the sealing function provided bythe potting compound 170 prevents leakage of fluids from inside thechamber or pipe (not shown), through the barrel 144, to outside of thechamber or pipe (not shown). In this example flow meter sensor 140, aseal 176 is also provided at the distal end of the barrel 144 to preventleakage of a fluid that is being measured for flow rate from leakinginto the barrel 144 to supplement the sealing function of the pottingcompound 170. The seal 176 can be made of, for example, glasses (frittedor glaze), metals (brazed, reflowed, or pressed fit), or ceramics(cements or press fit).

The electrical connections of the wires in the cable 30 to the contactterminals 164, 165, 166, 167 in the example flow meter sensor 140 (FIGS.22-25) can be made in the same way as the electrical connections 48, 49shown in FIG. 14A and described above, although other suitableconnections can also be used. Core 156, electrical conductors 156,thermal resistive element 168, ceramic or potting compound 170, andshield 145 can be made with any of the respective materials describedabove for the cores, electrical conductors, thermal resistive materials,and shields in other embodiments described above.

The example flow rate sensor embodiments described above can also beused the sensing the level of a fluid in a container or chamber (notshown). For example, a liquid will conduct heat away from the thermalresistive element 123 of the transducer 122 faster and more efficientlythan air or some other gas. Therefore, if the thermal resistive element123 is positioned at a level in the container or tank that is above aliquid in the container or chamber, thus in air or other gas, the air orother gas will not conduct heat away from the thermal resistive element123 very fast or efficiently, so the electrical resistance of thethermal resistive element 123 will be higher than if the thermalresistive element 123 was submerged in the liquid. Then, if the liquidin the container or chamber rises to a high enough level to contact thethermal resistive element 123 or to contact the optional heat transfermaterial discussed above (not shown), the liquid will conduct heat awayfrom the thermal resistive element 123 faster and more efficiently thanthe air or other gas, which will be manifested in a detectable change involtage across the thermal resistive element 123 or a detectable changein current flow through the thermal resistive element 123 as explainedabove. Conversely, the liquid level in the container or chamber dropsbelow the level of the thermal resistive element 123, the change fromliquid in contact with the thermal resistive element 123 to air or othergas in contact with the thermal resistive element 123 is manifested as adetectable change in voltage or current, as explained above.

An example capacitive pressure sensor 210 for measuring gas pressures invery high temperature conditions is shown in FIGS. 26-29, In thisexample capacitive pressure sensor 210, the core 220 and electricalconductors 224, 225, 226, 227 can be made of the same respectivematerials as described above for the core 20 and electrical conductors24, 25, 26, 27 of the example sensor device 10 in FIGS. 1-14 above. Theelectrical connections of the electrical conductors 224, 225, 226, 227to electrically conductive wires 240 (only two of which are visible inFIG. 26) in this example capacitive, pressure sensor 210 for conductingsignals from the capacitive pressure transducer 222 to the capacitancemeasurement electronics 290 can be the same as the electricalconnections of electrical conductors 24, 25, 26, 27 to the electricallyconductive wires 40, 42, 44, 46 of the example sensor device 10described above and shown in FIGS. 1-14A, although other electricalconnection techniques could be used. An optional shield 218 shown inFIG. 26 surrounds and encloses the core 220 and capacitive pressuretransducer 222 for protection. The shield 218 can be made of the samematerials as described above for the shield 18 in the sensor 10. Also,the shield 218 has a hole 217 extending from the interior of the shield218 to the exterior of the shield 218 so that fluid pressure inside theshield 218 can equalize with fluid pressure outside of the shield 218for measurement by the capacitive pressure transducer 222. The fittings214 configured, for example, as externally threaded pipe adapters,provide a mounting structure for mounting the probe 212 in a wall of achamber (not shown) or pipe (not shown) so that the probe 212 extendsinto such chamber or pipe in order to measure a pressure of a fluid insuch chamber or pipe. Again, other types of fittings, for example,welded, flanged, machined, or adhered fittings instead of threadedfittings can be used instead of threaded fittings.

An example capacitive pressure transducer 222 for the capacitivepressure sensor 210, as illustrated in FIGS. 28 and 29, can be madeentirely with materials that can withstand the very high temperaturesdescribed above, i.e., as high as 1,800° C. Therefore, the capacitivepressure transducer 222 can be placed in the distal end of the probe212, as shown in FIG. 22, where the very high temperature gases forwhich pressure is to be measured are located (see, e.g., the temperatureranges illustrated in FIG. 20), while the capacitance signalconditioning electronics 290 are placed outside of the chamber or pipe(not shown) that contain the very high temperature gases. Accordingly,the example capacitive pressure transducer 222 comprises a ceramichousing 252, which includes a resiliently deformable, ceramic membrane254, which encloses and hermetically seals a space 256. The housing 252is supported above the core 220 by one or more spacers, for example,spacers 258, 260, at least one of which is electrically conductive toprovide an electrical connection between an electrode 264 on themembrane 254 and an electrical conductor, e.g., the electrical conductor227, on the core 220 as described in more detail below. The membrane 254can be formed as an integral part of the housing 252, or it can beformed separately and then adhered or otherwise attached to the housing252 to enclose the space 256. When fluid pressure outside the housing252 and space 256 increases, such increased pressure causes the membrane254 to flex or deform toward or into the space 256 as illustrated, forexample, in FIG. 29. Conversely, decreased pressure outside the housing252 causes the membrane 254 to flex or deform away or outwardly from thespace 256. A first electrode 262, for example, a thin conductivematerial, is formed on or attached to the core 220 a distance spacedapart from the membrane 254. A second electrode 264, for example, a thinconductive material, is formed on or attached to the membrane 254 andflexes or deforms in conformance with the membrane 254 toward or awayfrom the first electrode 262 according to the fluid pressure outside ofthe space 256. As such, the first and second electrodes 262, 264 formand function as a variable electrical capacitor, as indicateddiagrammatically in FIGS. 28 and 29 by the capacitor symbol 266. Thecapacitance of the capacitor 266 varies as a function of the distancebetween the first and second electrodes 262, 264, which varies as afunction of fluid pressure outside of the housing 252 pressing on themembrane 254. An optional dielectric material 268 can be positionedbetween the first and second electrodes 262, 264 to increase thecapacitance between the first and second electrodes 262, 264. Such adielectric material 268 has to be able to withstand the very hightemperatures of the fluid for which the pressure is being measured bythe capacitive pressure sensor 210. Examples of such dielectricmaterials may include, but are not limited to, alumina, beryllium oxide,magnesia, halfnia, and barium titanate.

In the example capacitance pressure transducer 222 illustrated in FIGS.28 and 29, the second electrode is formed or attached on the surface ofthe membrane 254 that is opposite the hermetically sealed space 256,i.e., the surface of the membrane 254 that is outside of thehermetically sealed space 256. The first electrode 262 is connectedelectrically to, or is an extension of, one of the electricalconductors, e.g., the electrical conductor 224, on the core 220. Thesecond electrode 264 is connected electrically to another one of theelectric conductors, e.g., the electrical conductor 227, on the core 220via the spacer 260, which is an electrically conductive material, suchas any of the Noble or refractory metals or alloys mentioned above thatcan withstand the very high temperatures of the fluid for which thepressure is being measured. Therefore, the variable capacitor 266 can becharged and discharged through the two electrical conductors 224, 227,and the capacitance of the variable capacitor 266 can be detected andmeasured electrically by any of a number of techniques known to personsskilled in the art. For example, but not for limitation, oscillatorbased, charged based, timer based, and bridge based analog electricalsystems as well as variety of digital based systems known to personsskilled in the art can be used to detect and measure the capacitance ofthe sensor. Specific values of pressure for specific values of measurecapacitance can be determined empirically and used for outputtingpressure measurements from the capacitive pressure transducer 222.

The housing 252, including the membrane 254, can be made with any of theceramic materials as described above that can withstand the very hightemperatures of the gases for which pressure is to be measured with thecapacitive pressure transducer 222. In order to provide the electricallyconductive components and interconnections of the capacitive pressuretransducer 222 as described above and to provide a very small, preciselycontrolled gap between the first and second electrodes 262, 264, e.g.,in a range of 0.5 to 50 micrometers, for a practically sized transducer222 with enough capacitance to provide accurate pressure measurements,the capacitive pressure transducer 222 can be constructed withultrasonic, thermosonic, or thermocompression flip chip bondingtechniques. Pressure, heat, or ultrasonic energy can then be applied tothe spacers 258, 260 to form continuous electrical connection to theelectrical conductor 227 while precisely controlling the desired gapbetween the first and second electrodes 262, 264. The temperaturecapability of the joint is largely a function of the maximum usetemperature of the materials used. For example, in the case of silver,gold, or platinum, that maximum temperature, thus temperature capabilityof the joint, would be the melting temperature of the silver, gold, orplatinum. Platinum would max out at about 1,760° C. For other materials,for example refractories, the temperature capability of the joint wouldbe the temperature at which complete oxidation would occur.

As shown in FIGS. 26 and 27, a temperature transducer 270 can beprovided on the core 220 for temperature compensation. The temperaturetransducer 270 can, but does not necessarily have to, be the same as orsimilar to any of the temperature transducers described above,Temperature compensation is provided, because the volume of the space256 in the housing 252 varies as a function of temperature according tothe Ideal Gas Law, i.e., when held at a given pressure, the volume of agas is directly proportional to the temperature of the gas. Therefore, adecrease in temperature, even without a change in pressure outside ofthe housing 252, will cause the membrane 254 to flex into the space 256,which will decrease the capacitance between the first and secondelectrodes 262, 264. Conversely, an increase in temperature will causethe membrane 254 to Ilex outwardly away from the space 256, which willincrease the capacitance between the first and second electrodes 262,264. Inclusion of a temperature transducer 270 allows the effect oftemperature on capacitance to be determined empirically and thecapacitance measurements to be compensated in a manner that providesaccurate pressure measurements, regardless of temperature, according toprinciples and with analog or digital circuits that are conventional andunderstood by persons skilled in the art.

To minimize capacitance measurement errors due to unknown capacitancesto ground, spurious voltages, and capacitances from shielding in cables,the capacitance signal conditioning electronics 290 for the examplecapacitive pressure sensor 210 in FIG. 26 are provided close to thecapacitive pressure transducer 222, for example, in a ceramicelectronics encasement 292 attached to the fittings 214. The packagingof the capacitive pressure sensor 210 constructed with materials thatcan withstand the very high temperatures, as described above, can becomplemented by constructing the signal conditioning electronics 290with high temperature components, including ceramic multi-chip modules(MCMs), high temperature PCBs, high temperature passive devices(resistors, and capacitors), and high temperature silicon carbide (SiC)and silicon on insulator (SOI) active devices (amplifier, diodes,microcontrollers, etc.), which is an advantage due to benefit of havingsignal conditioning electronics close to the sensor element which canimprove sensor sensitivity and reduce noise. Therefore, the entirecapacitive pressure sensor 210 can withstand and operate reliably insuch very high temperature conditions.

An alternate example heat-resistant capacitive pressure sensor 310 shownin FIGS. 30-32 is not only capable of withstanding and functioning invery high temperatures, but is also resistant to corrosive fluids. Asillustrated in FIG. 30, the capacitive pressure sensor 310 comprises acapacitive pressure transducer 312 mounted on the distal end 314 of aprobe 316, the proximal end 315 of which extends from an electronicsencasement 318 that houses capacitive signal conditioning electronics(not shown). The electronics encasement 318 and the capacitive signalconditioning electronics can be the same as, or similar to, the ceramicelectronics encasement 292 and capacitive signal conditioningelectronics 290 shown in FIG. 26 and described above. The probe 316 cancomprise a mineral insulated cable 320 that is corrosion resistant andcan withstand very high temperatures. Such mineral insulated cables arewell-known to persons skilled in the art and commercially available frommyriad manufacturers and suppliers. The mineral insulated cable 320shown in FIGS. 30-32 comprises four electric conductors 322, 324, 326,328, but only two of the electric conductors 322, 324 are used for theexample capacitive pressure transducer 312 as will be explained in moredetail below. The other two electric conductors 326, 328 can be used forother purposes, for example, a temperature sensor, if desired.

Referring now primarily to FIGS. 31 and 32, the example capacitivepressure transducer 312 comprises a first pressure-sensitive element 330and a second pressure-sensitive element 332 disposed in juxtaposedrelation to each other. Each of the first and second pressure-sensitiveelements 330, 332 comprises a housing, e.g., first housing 334 andsecond housing 335, respectively, that encloses and hermetically seals aspace, e.g., a first space 336 and a second space 337, respectively. Oneside of the first housing 334 includes an elastic, resilientlydeformable membrane 338, which can be formed as an integral part of thefirst housing 334, or the first membrane 338 can be formed separatelyand then welded, adhered, or otherwise attached to the first housing 334to enclose the first space 336. Similarly, one side of the secondhousing 335 includes an elastic, resiliently deformable membrane 339,which can be formed as an integral part of the second housing 335, orthe second membrane 339 can be formed separately and then welded,adhered, or otherwise attached to the second housing 335. Accordingly,the respective first and second membranes 338, 339 are positioned injuxtaposed, closely spaced apart relation to each other, as indicated bythe distance D in FIG. 32, to form a capacitor as will be explained inmore detail below. An optional spacer 340 positioned between theperipheral, interfacing surfaces of the first and second housings 334,335 provide support to the respective pressure-sensitive elements 332,334, thus structural stability to the capacitive pressure transducer312. For structural integrity in corrosive, high temperature fluids, thefirst and second housings 334, 335, including the first and secondmembranes 338, 339, can comprise any of a variety of metals that canwithstand very high temperatures as discussed above and that areresistant to corrosion. For the example capacitive pressure transducer312, such metals for the first and second housings 334, 335 are alsoelectrically conductive to form a capacitor as will be explained in moredetail below. Such metals may include any of the Noble or refractorymetals or alloys mentioned above that can withstand the very hightemperatures of the fluid for which the pressure is being measured. Inlieu of metals, the first and second membranes 338, 339 can beelectrically conductive ceramics or metal coated insulating materials,such as metal coated ceramics, metal coated crystalline materials (e.g.,metal coated sapphire or metal coated silica), or metal coated amorphouscrystalline materials (e.g., metal coated amorphous sapphire or metalcoated amorphous silica). Also, the respective first and secondmembranes 338, 339 can be dished toward each other inside the spacer 340as illustrated in FIGS. 31 and 32 for compactness, e.g., for positioningthe first and second membranes 338, 339 in closely spaced- apartrelation to each other as needed for particular pressure and capacitanceranges, while also accommodating the spacer 340 between the first andsecond pressure-sensitive elements 332, 334. Accordingly, the convexlydished shape of the first and second membranes 338, 339 enables use of aspacer 340 that is thicker than the gap or distance D between the firstand second membranes 338, 339, which enhances ease of fabrication andassembly of the capacitive pressure transducer 312. Since the first andsecond housings 334, 335 are electrically conductive to form acapacitance between them when a voltage is applied, as explained below,the spacer 340 is non-electrically conductive or otherwise electricallyinsulated to avoid electrical conduction between the first and secondhousings 334, 335 in order to maintain the capacitance between the firstand second membranes 338, 339.

As best seen in FIG. 32, a first one of the electric conductors of themineral insulated cable 320, e.g., the electric conductor 322, isconnected electrically to the electrically conductive metal or otherelectrically conductive material of the first housing 334, and a secondone of the electric conductors of the mineral insulated cable 320 isconnected electrically to the electrically conductive metal or otherelectrically conductive material of the second housing 335. The firstand second metal housings 334, 335. including the first and secondmembranes 338, 339 can comprise an electrically conductive material,such as any of the Noble or refractory metals or alloys or otherelectrically conductive materials mentioned above that can withstand thevery high temperatures of the fluid for which the pressure is beingmeasured. Therefore, when a voltage is applied across the two electricconductors 322, 324, a capacitance is created between the first membrane338 and the second membrane 339, which, as explained above and shown inFIG. 32, are separated by the distance D. This capacitance relationshipbetween the respective first and second membranes 338, 339 of the firstand second metallic housings 334, 335 is illustrated diagrammatically inFIG. 33 with the capacitor symbol 342.

When fluid pressure outside the first and second housings 334, 335, thusoutside the first and second spaces 336, 337, increases, such increasedpressure causes the first and second membranes 338, 339 to flex ordeform toward or into the respective first and second spaces 336, 337,thus away from each other as illustrated diagrammatically, for example,in FIG. 34 by the arrows 341. Conversely, decreased pressure outside thehousings 334, 335 causes the first and second membranes 338, 339 to flexor deform away or outwardly from the respective spaces 336, 337, thustoward each other. As such, the first and second membranes 338, 339 formand function as a variable electrical capacitor, as indicateddiagrammatically in FIGS. 33 and 34 by the capacitor symbol 342. Thecapacitance of the capacitor 342 varies as a function of the distance Dbetween the first and second membranes 338, 339, which varies as afunction of fluid pressure outside of the first and second housings 334,335 pressing on the first and second membranes 338, 339. The distance Dis a value greater than zero that provides a detectable and measurablecapacitance that can be correlated empirically or otherwise to thepressure being measured and the first and second membranes 338, 339 haveindices of elasticity that facilitate changes in the distance D thatproduce detectable and measurable changes in the capacitance between thefirst and second membranes 338, 339, which correlate to changes in thepressure, as will be understood by persons skilled in the art. As can beappreciated from the diagrammatic illustrations in FIGS. 33 and 34 andthe related explanation above, the two juxtaposed membranes 338, 339moving away and toward each other as a function of pressure providesmore, twice as much change in the distance D, thus change incapacitance, for a given pressure change as compared to the capacitivepressure transducer 222 in FIGS. 26-29 that has only one membrane 254.Accordingly, the example capacitive pressure transducer 312 illustratedin FIGS. 30-34 can be more sensitive to pressure changes than thecapacitive pressure transducer 222 illustrated in FIGS. 26-29.

Alternatively, the capacitive pressure transducer 312 can be made withnon- electrically conductive first and second housings 334′, 335′, forexample ceramic, non- conductive metal, or other non-conductivematerial, as illustrated diagrammatically in FIGS. 35 and 36. Suchnon-conductive housings 334′, 335′ can be the same or similar to thehousing 252 in the example capacitance pressure transducer embodiment222 shown diagrammatically in FIGS. 28 and 29. For example, a firstelectrode 344′ in the form of a thin, electrically conductive plate orcoating, e.g., a metal ink or film, is formed on or attached to theexternal surface of the first membrane 338′ of the non-electricallyconducting first housing 334′ to flex or deform in conformance with thefirst membrane 338′ as pressure outside the first housing 334′ changes.Similarly, a second electrode 345′ in the form of a thin, electricallyconductive plate or coating, e.g., a metal ink or film, is formed on orattached to the external surface of the second membrane 339′ of thenon-electrically conductive second housing 335′ to flex or deform inconformance with the second membrane 339′ as pressure outside the secondhousing 335′ changes. The first electric conductor 322 of the mineralinsulated cable 320 (FIGS. 30-32) is connected electrically to the firstelectrode 344′, and the second electrical conductor 324 is connectedelectrically to the second electrode 345′, so that a voltage applied tothe first and second electric conductors 322, 324 a capacitance 342across the distance D between the first and second electrode 344′, 3″45′that varies as a function of pressure change outside of the first andsecond housings 334′, 335′ as explained above and illustrated by thearrows 341 in FIG. 36. The optional spacer 340 positioned between theperipheral, interfacing surfaces of the first and second housings 334′,335′ sets the distance D and provides support, thus structural stabilityto the capacitive pressure transducer 312 as explained above.

As an alternative to the spacer 340, the capacitive pressure transducer312 can be provided with a potting or coating 346 to maintain thedistance D and provide the support and structural integrity for theceramic first and second housings 334′, 335′, as illustrateddiagrammatically in FIG. 37, or for the housings 334, 335 in FIGS. 30-34if desired. Where the housings 334′, 335′ are ceramic or made of anothermaterial that may be vulnerable to corrosive fluids, the potting orcoating 346 can also provide corrosion protection for such components.For example, a gold plated metal coating 346 can provide protectionagainst oxidation or other chemical reactions. Of course, some openingor passageway 348 has to be provided to expose the space between thefirst and second membranes 338′, 339′ to ambient pressure outside of thecapacitive pressure transducer 312 to enable the membranes 338′, 339′ toflex or deform under varying pressures outside of the transducer 312.

The example capacitive pressure sensor 310 described above isillustrated in FIGS. 38 and 39 mounted in a fitting 350 that can bescrewed into a mating fitting (not shown) in a pressure orfluid-containing vessel (not shown) in such a manner that the capacitivepressure transducer 312 can be positioned inside the pressure orfluid-containing vessel, where the capacitive pressure transducer 312 isexposed to a fluid, the pressure of which is to be measured ormonitored, inside the vessel, while the remainder of the probe 316,including the electronics encasement 318, are positioned outside of thevessel. In FIG. 40, the capacitive pressure sensor 310 is illustratedwith an optional sheath or shield 352 mounted in the fitting 350 aroundthe capacitive pressure transducer 312, which is hidden by the shield352. The optional shield 352 may be used, for example, to protect thecapacitive pressure transducer 312 from objects or debris in the vesselthat could damage the capacitive pressure transducer 312. The shield 352has a hole 354 in its distal end 356 to expose fluid and the capacitivepressure transducer 312 inside the shield 352 to the same pressures asthe fluid outside of the shield 352.

Another example capacitive pressure transducer 360 illustrated in FIGS.41 and 42 isolates the capacitor electrodes 362, 364 from fluids outsideof the capacitive pressure transducer 360, which may be beneficial, forexample, in situations where the fluid pressure to be measured ormonitored involves a corrosive fluid and there is a need or desire touse capacitor electrodes 362, 364, wires, and other electricalcomponents made of materials that maximize or enhance the electricalproperties of the capacitor regardless of the abilities of suchmaterials to resist corrosion, The example capacitive pressuretransducer 360 in FIGS. 41 and 42 comprises a housing 366 that enclosesand hermetically seals a space 368. A side of the housing 366 comprisesa resiliently deformable or flexible membrane 370 that will deform orflex in response to pressure changes outside of the housing 366 in apressure range to be measured or monitored with the capacitive pressuretransducer 360. The housing 366 and the membrane 370 comprise a materialthat is corrosion resistant, The capacitor (indicated by the capacitorsymbol 372) is formed by a first electrode 362 and a second electrode364 positioned inside the enclosed space 36$ and held apart from eachother by one or more standoff supports, e.g., standoff supports 374,376. At least one of the electrodes, e.g., first electrode 362, isresiliently deformable or flexible toward and away from the secondelectrode 364. A pusher 378, e.g., a pole, strut, or nub, in theenclosed space 368 extends from the inside surface 371 of the membrane370 to the first electrode 362. Therefore, when an external pressure(indicated in FIG. 42 by the pressure arrows 380) on the membrane 370causes the membrane 370 to deform or flex toward the first electrode362, the pusher applies a force to the first electrode 362 that deformsor flexes the first electrode toward the second electrode 364, therebychanging the capacitance between the first and second electrodes 362,364, Such change in capacitance is detectable on the lead wires 382, 384that are electrically connected, respectively, to the first electrode362 and second electrode 364.

Another example capacitive pressure transducer 360′ illustrated in FIGS.43-45 is a modification of the example capacitive pressure transducer360 in FIGS. 41 and 42. Essentially, the capacitive pressure transducer360′ can be the same as the capacitive pressure transducer 360, exceptfor the pusher 378′, which in the capacitive pressure transducer 360′does not extend all the way to the first electrode 360 in the entirepressure range of the fluid outside the housing 366 for which pressureis to be measured, As shown diagrammatically in FIG. 43, at theparticular pressure outside the housing 366 that exists in thisillustration, the pusher 378′ does not extend all the way from themembrane 370 to the first electrode 360, thus leaving a gap 386 betweenthe pusher 378 and the first electrode 362. That outside pressure, forexample, could be the same as the pressure inside the space 368, so thatthere is no differential pressure between the outside of the housing andthe inside of the housing, or there could be a differential pressure,but not enough to cause significant deformation or flexing of themembrane 370. In that condition, there is a distance DI between thefirst and second electrodes 362, 364 and a capacitance between the firstand second electrodes 362, 364 associated with that distance D1.

In FIG. 44, the example capacitive pressure transducer 360′ isillustrated with just enough pressure 380 outside the housing 366 tocause the membrane 370 to deform or flex inwardly enough to move thedistal end of the pusher 378 into contact with the first electrode 362,thus eliminating the gap 386 between the pusher 378 and the firstelectrode 362. In that condition, the distance D1 between the first andsecond electrodes 362, 364 is still the same as in FIG. 43, so thecapacitance between the first and second electrodes 362, 364 remainsunchanged, i.e., no response on lead wires 382, 384 from that pressurechange, as illustrated by the flat graph line 388 in the graph in FIG.46.

Then in FIG. 45, the example capacitive pressure transducer 360′ isillustrated with even more pressure 381 outside the housing 366, thuscausing the membrane 370 deform or flex even more. That additionaldeformation or flex in the membrane 370 causes the pusher 378 to pushthe first electrode 362 toward the second electrode 364, therebydecreasing the distance between the first and second electrodes 362, 364to a smaller distance D2 as illustrated in FIG. 45. That change in thedistance between the first and second electrodes 362, 364 from D1 inFIGS. 43 and 44 to the smaller D2 in FIG. 45 causes the capacitancebetween the first and second electrodes 362, 364 to increase asillustrated by the inclined graph line 390 in FIG. 46. This structureand resulting function of the capacitive pressure transducer 360′ inFIGS. 43-45 allows for the pressure-capacitance response to include apressure offset as illustrated in FIG. 46 or a pressure range that mustbe reached before the capacitance of the sensor changes. This featurecan be used, for example, to measure pressures in environments orvessels where the desired pressure measurement range is small and offsetfrom null.

Another example capacitive pressure transducer 360″ shown in FIGS. 46and 47 is similar to the capacitive pressure transducer 360′ of FIGS. 41and 42, but the space 368 is in communication with a reference pressureoutside of the housing 366. For example, the space 368 in the housing366 is shown diagrammatically in FIG. 46 as being connected by anaperture 367 to the ambient atmosphere 369 outside of the housing 366,while the external surface of the flexible membrane 370 is exposed tothe pressure 380 that is being sensed or measured. In FIG. 46, thepressure 380 is in a chamber 373 illustrated diagrammatically as theinterior of an enclosure 375. Accordingly, a pressure measurementprovided by the example capacitive pressure transducer 360″ in FIG. 46is a differential pressure between the pressure 380 in the chamber 373and the ambient atmosphere 369.

In FIG. 47, the example capacitive pressure transducer 360 is shown withthe space 368 connected by the aperture 367 to a different referencepressure (REF) illustrated diagrammatically by the block 377.Accordingly, in FIG. 47, a pressure measurement provided by the examplepressure transducer 360″ is a differential pressure between the pressure380 in the chamber 373 and the reference pressure (REF),

The reference pressure features illustrated diagrammatically in FIGS. 47and 47, e.g., the aperture 367, REF pressure 377, and chamber 373, canalso be applied to the capacitive pressure transducer 312 in FIGS. 30-40and to the alternative capacitive pressure transducers 360′ in FIGS.43-45, as will be understood by persons skilled in the art once theybecome familiar with the capacitive pressure transducers 360″ describedabove and illustrated diagrammatically in FIGS. 47 and 48.

An example rotation-insensitive flow meter sensor 410 that can withstandand function in very high temperature fluids is illustrated in FIGS.49-53. Rotation-insensitive in this description means essentially thatthe flow measurement outputs of this example flow meter are notsensitive to the rotational orientation of the meter with respect to thedirection of flow of the fluid. The example flow meter sensor 410 has aflow transducer 412 mounted on a distal end 414 of a probe 416, whichcomprises a mineral insulated cable 418 with a plurality of electricconductors, e.g., the four electric conductors 420, 422, 424, 426illustrated in FIGS. 49, 50, and 52. As best seen in FIGS. 52 and 53,the example flow transducer 412 comprises a sensing element 430 on aceramic substrate 432 mounted in a housing 434 made of materials, eitherceramic or metal, that can withstand the high temperatures of the fluidfor which flow rate is to be measured with flow meter sensor 410. In theexample flow transducer 412 in FIGS. 49-52, the housings 434 includes abase component 436 mounted on the distal end 414 of the probe 416 and amounting ring 438 for mounting the ceramic substrate 432 on the distalend of the flow meter sensor 410 substantially in a plane perpendicularto the longitudinal axis 440 of the probe 416. The sensing element 430is an electrically resistive material, the resistivity of which variesas a function of temperature. Many of such temperature-dependentresistive materials are commercially available from myriad manufacturersand distributors, including metallic inks and other metals and alloysthat can be printed, deposited, or otherwise placed on the ceramicsubstrate 432 to form the sensing element 430, for example platinum,gold, or other thermal resistive metals that can withstand the hightemperatures of the fluid for which flow rate is being measured,including any such metals or other thermal resistive materials asdescribed above,

In operation, the probe 416 and flow transducer 412 are positioned inthe flowing fluid to measure the flow rate of the fluid. Accordingly,the fluid flows over the exposed surface 442 of the ceramic substrate432 as indicated by the flow arrow 444 in FIGS. 49 and 51. At the sametime, a voltage is applied across the sensing element 430 on theinternal surface 443 of the ceramic substrate 430 by connecting theelectric conductors 420, 422 in the probe 416 to a voltage source (notshown). The voltage causes an electric current flow through the thermalresistive sensing element 430, which creates heat. The heat created inthe thermal resistive sensing element is conducted by the ceramicsubstrate 432 from the internal surface 443 to the exposed externalsurface 443, which is in contact with the flowing fluid 444, The flowingfluid 444 conducts heat away from the ceramic substrate 432, thus alsofrom the thermal resistive sensing element 430, i.e., cools theresistive sensing element 430. The cooling of the resistive sensingelement 430 changes the electrical resistance of the thermal resistivesensing element 430, which changes the voltage across or current flowthrough the resistive sensing element 430. Such changes can be detectedand measured as is well understood by persons skilled in the art. Thehigher the flaw rate of the flowing fluid 444, the more heat isconducted away from the ceramic substrate 432 and resistive sensingelement 430, all of which can be detected as a result of thecorresponding changes in resistivity of the thermal resistive sensingelement 430 as described above in relation to the other example flowmeter embodiments.

The housing 434 and ceramic substrate 432 isolate the thermal resistivesensing element 430 from the fluid, which may be important if the fluidis electrically conductive or corrosive to the thermal resistive sensingelement 430. The mounting ring 438 is preferably a thermal insulatingmaterial to prevent heat produced by the thermal resistive sensorelement 430 from being conducted into the housing 434 and probe 416instead of being conducted away by the flowing fluid 444, which wouldadversely affect the sensitivity and accuracy of the flow ratemeasurements obtainable with the flow meter sensor 410 as well as powerconsumption by the resistive sensor element 430. Other bands of thermalinsulating material (not shown) can also be included for this purposebetween the ceramic substrate 432 and the rest of the housing 434 orprobe 416. Also, fluid flow 444 in any direction that is perpendicularto the longitudinal axis 440 of the probe 416, i.e., which is parallelto the exposed surface 442 of the ceramic substrate 432, will conductheat away from the ceramic substrate 432 as effectively as fluid flow inany other direction that is perpendicular to the longitudinal axis 440.Therefore, unlike the flow meter embodiment in FIGS. 22-24, flow ratemeasurements with the flow meter sensor 410 in FIGS. 49-52 are notdependent on any particular rotational orientation of the flow metersensor 410, as long as the fluid flow is substantially perpendicular tothe longitudinal axis 440, thus substantially parallel to the exposedsurface 442 of the ceramic substrate 432, One or more temperaturesensor(s) 446, for example, thermocouples or other heat sensors, aremounted in the housing 434 to measure the ambient temperature of theflowing fluid for temperature corrections due to sensitivity of thethermal resistive sensor element 430 as is understood by persons skilledin the art. The thermal insulating ring 438 also inhibits heat producedby the thermal resistive sensor element 430 from affecting temperaturemeasurements by the temperature sensors 446, which are important forobtaining accurate flow rate measurements with corrections fortemperature effects.

Another example rotation-insensitive flow meter sensor 450 shown inFIGS. 54-57 is much the same as the example rotation-insensitive flowmeter sensor 410 in FIGS. 49-52, except additional protection isprovided for the ceramic substrate 432 that holds the thermal resistivesensor element 430, which can be the same as the thermal resistivesensor element 430 in FIGS. 50 and 53. For example, as best seen in FIG.57, the ceramic substrate 432 of the flow rate transducer 452 is brazedto a metal end plate or cladding 454, which is joined (by welding, forexample) to a thermal insulating metal ring 456 that is part of thehousing 458. The base component 460 of the housing 458 is a cylindricalmetal sleeve on which the insulating metal ring 454 is mounted.Accordingly, all parts of the flow rate transducer 452 which are exposedto the fluid are metals that can withstand the very high temperatures ofthe fluid in which the flow meter sensor 450 is to be used and resistantto corrosion by the fluid in which the flow meter sensor 450 is to beused. The metal end plate 454 is a good thermal conductor for efficientconduction of heat produced by the thermal resistive sensor element 430to the fluid flowing on or over the metal end plate 454, for example,molybdenum, a thermally conductive stainless steel, or thermallyconductive nickel alloy. The base component 460 of the housing 458 isalso a good thermal conductor metal to conduct heat from the fluid tothe temperature sensor 462, for example, a thermocouple or othertemperature sensor device, mounted in the base component 460, to providean accurate measure of ambient fluid temperature. The ring 456, however,is a thermally insulating metal to prevent heat produced by the thermalresistive sensor element 430 from being conducted into or through theprobe 464 instead of through the metal end plate 454 and into the fluidflowing on or over the metal end plate 454. Accordingly, the ceramicsubstrate 432 is not in contact with the fluid of which the flow rate isto be measured, which is important if the fluid is corrosive to theceramic substrate 430 and if there are chunks of hard material flowingin the fluid that could break the ceramic substrate 430. The electricconductors 420, 422 of the mineral insulated cable 466 are connected toopposite ends of the thermal resistive sensor element 430, and theelectric conductors 424, 426 are connected to the temperature sensor 462as in the previously discussed flow meter sensor 410 in FIGS. 49-52.

An example fluid flow sensor 470 for detecting mass flow rate as well asflow direction, including fluid flows in very harsh environments, e.g.,very high heat, corrosive fluids, etc., is illustrated in FIGS. 58-60.With primary reference initially to FIGS. 58 and 59 the fluid flowdetector 470 comprises a directional flow transducer 472 mounted on abase 474 and optionally enclosed in a protective sheath 476. A portionof the sheath 476 is cut away in FIG. 58 to reveal a portion of the flowtransducer 472. The flow transducer 472 comprises a heater 478 in thecenter of a core material 480. At least three temperature sensors 484,486, 488 are located on or near the peripheral surface 490 of the corematerial 480 and spaced apart angularly in relation to each other aroundthe core material 480 and radially outward from the heater 478. Suchtemperature sensors can be thermocouples, resistance temperaturedetectors, or other commercially available temperatures that canwithstand the temperatures in which the flow is to be measured, and suchtemperature detectors are available commercially in a variety of shapesand sizes, as is well-known to persons skilled in the art, thus need notbe described in more detail here. In one example embodiment illustratedin FIGS. 58-60, the directional flow transducer 470 comprises acylindrical core material 480, and the heater 478 is a tubular heaterthat extends coaxially along a longitudinal axis 482 of the cylindricalcore material 480, Such tubular heaters are available commercially in avariety of sizes and with a variety of heating components, thus need notbe described in more detail here. The core material 480 can be a pottingmaterial, a metal, or any other heat conductive material.

In operation, the flow sensor 470 is placed in a flow of fluid, forexample, in a wind, flowing gas, or flowing liquid, as indicated by thewind flow arrows 492 in FIG. 58. Electric current is provided to theheater 478 via the electric cord 494, and heat produced by the heater478 spreads radially outward from the heater 478 by conduction throughthe core material 480. If no cooling wind is present, all of thetemperature sensors 484, 486, 488 will read the same temperature,assuming all of the temperature sensors are the same radial distancefrom the heater 478. However, if there is a wind present, as illustrateddiagrammatically in FIG. 59, more of the heat in the core material 480will be conducted away by the wind on the windward side of the corematerial 480 than on the leeward side, Therefore, the windward side ofthe core material 480 will be cooler than the leeward side, and thetemperature sensor(s) on the windward side will have lower readings thanthe temperature sensor(s) on the leeward side, while temperaturesensor(s) between the windward side and the leeward side will havetemperature readings higher than temperature sensors on the windwardside and lower than temperature sensors on the leeward side, asillustrated by the temperature T1 of the temperature sensor 484, thetemperature T2 of the temperature sensor 486, and the temperature T3 ofthe temperature sensor 486 in FIG. 60. The difference between the lowesttemperature reading and the temperature of the heat source (i.e., at theheater 478) can be correlated to flow rate, and the differences amongthe plurality of temperature sensors 484, 486, 488 can be correlated toflow direction. An additional temperature sensor 479 can be placed inclose proximity to, or integrated into, the heater 478 for measuring thetemperature at the heater 478. Another temperature sensor 481 can beplaced external to the flow transducer 472 in the flowing fluid 492 formeasuring ambient temperature of the flowing fluid 492 for use as areference for determining an accurate flow rate. Temperaturemeasurements from either the temperature sensor 479 or the temperaturesensor 481 can be used in flow rate calculations along with thetemperature measurements with the temperature sensors 484, 486, 488,because flow rate calculations are based on a temperature differentialbetween the temperature sensors 484, 486, 488 and a referencetemperature, and the reference temperature can be the temperature at theheater 478 (e.g., measured by the temperature sensor 479) or thetemperature of the flowing fluid 492 (e.g., measured by the temperaturesensor 481).

As mentioned above, the core material 480 can be a potting material, aceramic, a metal, or other material that is a good heat conductormaterial. The core material 480 will conduct heat efficiently from thebeater 478 radially outward to the peripheral surface 490 of the corematerial 480 to be dissipated into the flowing fluid (e.g., wind,flowing gas, or flowing liquid) and thereby differentially cool more onthe windward side than on the leeward side. Choice of material for thecore material 480 may be based on particular application conditions,including, for example, temperature range, range of flow rates to bemeasured, and fluid properties such as density and thermal conductivity.Some suitable materials include ceramics (for example, aluminum oxide ormagnesium oxide) and metals (for example, stainless steels, silver,copper, aluminum, and nickel alloys).

The optional sheath 476 can be provided to protect sensitive components,such as the heater 478 and temperature sensors 484, 486, 488, from harshenvironment and environmental hazards. For example, the sheath 476 cancomprise a metal or ceramic that can withstand the high temperatureranges or corrosive conditions in which the fluid flow sensor 470 isused. The sheath should also comprise a good thermal conductor materialso as to efficiently conduct heat from the core material 480 to theflowing fluid (e.g., wind, flowing gas, or flowing liquid) that contactsthe external surface of the sheath 476.

The example fluid flow sensor 470 illustrated in FIGS. 58-60 can onlysense flow rate and flow direction in the 2-dimentional plane that isnormal to the longitudinal axis 482 of the sensor, but the operativeconcept and principles also apply to 3-dimensional flow. For example, aheat source (e.g., heater) in the middle of a spherical core material(not shown) with multiple sensors dispersed at regular intervals aroundthe spherical core material could be used to sense flow rate and flowdirection in a 3-dimensional manner,

Persons skilled in the art can provide electric circuits and equipmentfor powering the heater 478 and for reading temperatures from thetemperature sensors 484, 486, 488 and can select appropriate corematerials for particular applications (e.g., operating temperatureranges, fluid flow rate ranges, corrosiveness of flowing fluids, etc.)without undue experimentation, once they understand the principlesexplained above. Also, particular flow rates and directions forparticular flowing fluids to be measured with particular core materials,particular temperature sensors, and particular heaters and heatercapacities can be calibrated empirically as will be understood bypersons skilled in the art once they understand the principles explainedabove.

The foregoing description provides examples that illustrate theprinciples of the invention, which is defined by the claims that follow.The temperature, pressure, and flow rate detecting embodiments describedabove and shown in the drawings are examples, but not the onlyembodiments, that can be used with the sensor probe, core, and otherstructures described above. Once persons skilled in the art understandthe principles of this invention, such person will recognize that stillother embodiments of temperature, pressure, flow, and liquid leveltransducers or sensors as well as other types can also be used. Sincenumerous insignificant modifications and changes will readily occur tothose skilled in the art once they understand the invention, it is notdesired to limit the invention to the exact example constructions andprocesses shown and described above. Accordingly, resort may be made toall suitable combinations, subcombinations, modifications, andequivalents that fall within the scope of the invention as defined bythe claims. The words “comprise,” “comprises,” “comprising,” “include,”“including,” and “includes” when used in this specification, includingthe claims, are intended to specify the presence of stated features,integers, components, or steps, but they do not preclude the presence oraddition of one or more other features, integers, components, steps, orgroups thereof. Also, directional terms, such as “upwardly,”“downwardly,” “on,” “off,” “over,” “under,” “above,” “below,” etc., mayand sometimes do relate to orientation of components and features asillustrated in the drawing sheets, and are not used to require anyparticular physical orientation or any limitation on orientation of thedevice or component in actual use.

1. A sensor device for sensing pressure of a very high temperaturefluid, comprising: a transducer comprising a first pressure sensitiveelement and a second pressure sensitive element; wherein the firstpressure sensitive element comprises a first housing that encloses andhermetically seals a first space, one side of the first housingincluding a resiliently deformable and electrically conductive firstmembrane; wherein the second pressure sensitive element comprises asecond housing that encloses and hermetically seals a second space, oneside of the second housing including a resiliently deformable andelectrically conductive second membrane; and. wherein the first pressuresensitive element and the second pressure sensitive element arepositioned adjacent to each other with the first membrane and the secondmembrane positioned in juxtaposed relation to each other a spaceddistance apart from each other so as to form a capacitor.
 2. The sensordevice of claim 1, wherein the first housing, including the firstmembrane, comprises an electrically conductive metal or metal alloy thatcan withstand very high temperatures, and the second housing, includingthe second membrane, comprises an electrically conductive metal or metalalloy that can withstand very high temperatures.
 3. The sensor device ofclaim 1, wherein the first housing comprises a ceramic material that canwithstand very high temperatures and the first membrane comprises anelectrically conductive metal or metal alloy that can withstand veryhigh temperatures, and wherein the second housing comprises a ceramicmaterial that can withstand very high temperatures and the secondmembrane comprises an electrically conductive metal or metal alloy thatcan withstand very high temperatures.
 4. The sensor device of claim 3,wherein the first membrane comprises a ceramic material that canwithstand very high temperatures and an electrically conductive metal ormetal alloy plate or coating, which can also withstand very hightemperatures, formed on or attached to an external surface of the firstmembrane, and wherein the second membrane comprises a ceramic materialthat can withstand very high temperatures and an electrically conductivemetal or metal alloy plate or coating, which can also withstand veryhigh temperatures, formed on or attached to an external surface of thesecond membrane.
 5. The sensor device of claim 1, including a spacerpositioned between respective peripheral, interfacing surfaces of thefirst and second housings.
 6. The sensor device of claim 5, wherein thespacer comprises a putty or potting material.
 7. A capacitive pressuretransducer, comprising: a housing that encloses a space, a side of thehousing comprising a resiliently deformable or flexible membrane thatdeforms or flexes in response to pressure changes outside of the housingin a pressure range to be measured or monitored, wherein the housing andthe membrane comprise a material that is corrosion resistant; acapacitor formed by a first electrode and a second electrode positionedinside the enclosed space and held apart from each other by one or morenon-electrically conductive stand- off supports, the first electrodebeing resiliently deformable or flexible toward or away from the secondelectrode; and a pusher in the enclosed space that extends from themembrane toward the first electrode.
 8. The capacitive pressuretransducer of claim 7, wherein the pusher extends from the membrane tothe first electrode.
 9. The capacitive pressure transducer of claim 7,wherein the enclosed space is in fluid-flow communication with areference pressure outside of the enclosed space.
 10. A method ofmeasuring pressure of a very high temperature fluid, comprising: placinga transducer in the fluid, wherein the transducer comprises: (i) a firstpressure sensitive element, wherein the first pressure sensitive elementcomprises a first housing that encloses a first space, and wherein oneside of the first housing includes a resiliently deformable andelectrically conductive first membrane; and (ii) a second pressuresensitive element disposed adjacent to the first pressure sensitiveelement, wherein the second pressure sensitive element comprises asecond housing that encloses a second space, and wherein one side of thesecond housing includes a resiliently deformable and electricallyconductive second membrane, and further, wherein the second pressuresensitive element is positioned and oriented such that the secondmembrane is juxtaposed to the first membrane with a distance between thefirst membrane and the second membrane; applying a voltage across thefirst membrane and the second membrane; measuring capacitance betweenthe first membrane and the second membrane; and determining the pressureof the fluid by comparing the capacitance to a predetermined correlationof capacitance measurements to pressures,
 11. A flow meter sensor forsensing flow of a high temperature fluid, comprising: a transducercomprising a housing that encloses a space, said housing comprising amaterial that can withstand high temperatures of the fluid for whichflow is sensed, including one side of the housing comprising a ceramicsubstrate with a surface outside of the housing and another surface thatis inside the housing; a sensor element mounted on the surface of theceramic substrate that is inside the housing, said sensor elementcomprising an electrically resistive material, the resistivity of whichvaries as a function of temperature, and which can withstand the hightemperatures of the fluid for which flow is sensed; a sensor elementmounted to the housing, said sensor element comprising a temperature-sensitive set of materials which can withstand the high temperatures ofthe fluid for which flow is sensed.
 12. The flow meter sensor of claim11, wherein the material of the housing is ceramic,
 13. The flow metersensor of claim 11, wherein the transducer is mounted on a distal end ofa probe that has a longitudinal axis, the ceramic substrate beingpositioned in a plane that is substantially perpendicular to thelongitudinal axis of the probe,
 14. A flow meter sensor for sensing flowof a high temperature fluid, comprising: a transducer comprising ahousing that encloses a space, said housing comprising a corrosionresistant material that can withstand high temperatures of the fluid forwhich flow is sensed, including one side of the housing comprising aceramic substrate with a surface outside of the housing and anothersurface that is inside the housing, and a plate or cladding comprising acorrosion resistant material that can withstand the high temperatures ofthe fluid for which flow is to be sensed with the flow meter sensor; anda sensor element mounted on the surface of the ceramic substrate that isinside the housing, said sensor element comprising an electricallyresistive material, the resistivity of which varies as a function oftemperature, and which can withstand the high temperatures of the fluidfor Which flow is sensed; a sensor element mounted to the housing, saidsensor element comprising a temperature-sensitive set of materials whichcan withstand the high temperatures of the fluid for which flow issensed.
 15. The flow meter sensor of claim 14, wherein the corrosionresistant material comprises a metal or metal alloy that can withstandthe high temperatures of the fluid for which flow is to be sensed withthe flow meter sensor.
 16. A fluid flow sensor for detecting mass flowrate and flow direction of a fluid flow, comprising: a heater positionedin a core material that has a longitudinal axis and a peripheralsurface; and at least three temperature sensors located at or near theperipheral surface of the core material and spaced apart angularly inrelation to each other around the heater and spaced radially outwardfrom the heater.
 17. The fluid flow sensor of claim 16, wherein the corematerial is cylindrical and has a longitudinal axis, and wherein theheater is an elongated heater that extends coaxially through thecylindrical core material.
 18. The fluid flow sensor of claim 16,wherein the core material is a heat conductive material.
 19. The fluidflow sensor of claim 16, wherein the core material is a material thatcan withstand very high temperatures.
 20. The fluid flow sensor of claim19, wherein the core material comprises a ceramic.
 21. The fluid flowsensor of claim 19, wherein the core material comprises a metal.
 22. Thefluid flow sensor of claim 16, including a protective sheath around theperipheral surface of the core material.
 23. The fluid flow sensor ofclaim 22, wherein the protective sheath comprises a material that canwithstand highly corrosive fluids for which flow is to be sensed.
 24. Amethod of detecting mass flow rate and flow direction of a fluid,comprising: positioning a core material in the flowing fluid, the corematerial having a peripheral surface and a center; producing heat in thecore material with a heater positioned at the center of the corematerial; measuring temperatures at each of at least three locations ator near the peripheral surface of the core material with at least threetemperature sensors positioned respectively at the three locations,wherein the three temperature sensors are spaced apart angularly inrelation to each other and radially outward from the heater; andindicating windward direction of the flowing fluid in relation to thecore material as a side of the core material on which the temperaturemeasurements are lower than the temperature measurements on other sidesof the core material.
 25. The method of claim 24, including measuringtemperature at the heater and determining mass flow rate as a functionof a difference between temperature of the heater and the lowesttemperature reading from the temperature sensors.